Our previous work has demonstrated that the immunosuppressive drug rapamycin selectively affects the CsA-resistant pathway. We have shown that activation of T cells by interleukin-12 (IL-12) plus IL-18 is resistant to CsA, but sensitive to rapamycin. As the intracellular target of rapamycin is mTOR (mammalian target of rapamycin), we are investigating the mechanism of activation of mTOR during T cell activation. Our preliminary data indicate that PKC- plays an important role in turning on mTOR downstream signaling. We have shown that translocation of PKC- to the plasma membrane precedes the appearance of phospho-p70S6K1, an mTOR downstream signaling molecule, in the cytoplasm. Knockdown of PKC- blocks mTOR activation. We are currently investigating the mechanism involved in PKC--mediated mTOR activation. Role of mTOR in T cell differentiation has been well documented. We specifically interested in the role of p70S6K1 in T cell differentiation. Our preliminary data indicate that p70S6K1 plays an important role in T helper (Th) 17 cell differentiation, whereas the differentiation of Th1, Th2, or T regulatory (Treg) cells were unaffected by p70S6K1. We are investigating the molecular mechanisms involved in the role of p70S6K1 in the differentiation of Th17 cells. It has been shown recently that mitochondrial oxidation plays an important role in T cell activation. It has been known that mTOR influences mitochondrial metabolism. To investigate further the role of mTOR in mitochondrial oxidation, we are studying the effect of oxygen concentration on the activation of T cells using splenic T cells from wild type (WT) and p70S6K1 knockout (KO) mice cultured in 21 versus 5% O2 incubator. Our preliminary data indicate that p70S6K1 plays an important role in sensing O2 concentration available during culture condition. We have also observed the differential production of reactive oxygen species (ROS) by WT versus p70S6K1 KO T cells cultured in two different O2 concentrations. Since ROS is the principal actor in the free radical theory of aging, and p70S6K1 has been shown to be a determinant of mammalian aging, we are interested in investigating the molecular mechanisms underlying the differential production of ROS versus mitochondrial respiration by WT versus p70S6K1 T cells.